The Cr3+-rich ettringite was found in mineral assemblages of the Ma’aleh Adumim area (Judean Desert). Single-crystal XRD analysis of one Cr-free and two Cr3+-rich samples and their structure determination and refinement indicate that the Cr-rich crystals (with Cr/(Cr+Al) to 0.3) preserve the symmetry and metrics of ettringite. The Ca–O bonding network was found out to undergo differentiation with increasing of Cr3+ concentration at octahedral M sites. The compression of Ca2 and expansion of Ca1 polyhedra sub-networks correlates with the degree of Cr3+→Al substitution